1. Field of the Invention
The present invention relates to an endoscope system, a processor device thereof, and a method for displaying an endoscopic video image.
2. Description Related to the Prior Art
Endoscopy using an endoscope system is widely employed in a medical field. The endoscope system is constituted of an electronic endoscope, a light source device, a processor device, a monitor, and the like. In recent years, there is known an endoscope system that is provided with not only a normal mode (normal light observation mode) for observing an entire image of the inside of a body cavity under white light having a wide wavelength band, but also a special mode (special light observation mode) for performing observation from various viewpoints using special light in a specific narrow wavelength band.
In the normal mode, normal light such as xenon light in the wide wavelength band is applied to an internal body portion, and a color image sensor captures the light reflected from the body portion. A color video image obtained by the image sensor is displayed on the monitor. In another technique, as described in Japanese Patent Laid-Open Publication No. 08-068952, the normal light is color-separated into three colors of light, and an endoscope system sequentially applies the three colors of light to the internal body portion. A monochrome image sensor captures the light reflected therefrom by a frame sequential method. Three color frame images obtained thereby are merged into a full color video image.
In the special mode, a blood vessel pattern obtaining technique is known in which a blood vessel in a specific depth is enhanced using the special light having a wavelength at which hemoglobin has a high light absorption coefficient. Also, there is known an oxygen saturation level obtaining technique. In this technique, a plurality of types of special light that have different wavelengths including a wavelength at which the light absorption coefficient much differs between oxygenated hemoglobin and deoxygenated hemoglobin are sequentially applied to the internal body portion. The reflected light therefrom is captured by a sequential method to obtain a plurality of frame images. The oxygen saturation level is calculated from the plurality of frame images. The above techniques facilitate finding out a lesion such as cancer that is hard to spot under the normal light.
In the case of capturing the plurality of frame images by the sequential method under irradiation with the plurality of types of special light, each individual frame image is captured at different timing. Thus, if displacement occurs among the frame images due to various movements such as a shake of a head assembly of the electronic endoscope and a body motion, artifact arises in an endoscopic image produced from the frame images. As a measure against the artifact, in the system of the Japanese Patent Laid-Open Publication No. 08-068952, the single endoscopic image, which is produced from the RGB three frame images obtained by the frame sequential method, is displayed in color, if the movement is small. The display is switched into monochrome, if the movement is large so as to cause color deviation in the color display.
In the system of the Japanese Patent Laid-Open Publication No. 08-068952, the switching between the color display and the monochrome display is performed manually by keyboard input. This switching operation is often a burden to a doctor who steering the electronic endoscope. To reduce the burden on the doctor, another hand, for example, a switching assistant is required.